Steady-state absorption spectra

Figure 8.11a shows steady-state absorption spectra of the CdTe quantum dots in water. Each spectrum in the figure exhibits a distinct peak at a different band corresponding to its size, indicating that all of these suspensions include mono-dispersed nanocrystals. This mono-dispersibility is also supported by their emission spectra with different peak bands corresponding to particle size, as in Figure 8.11b. 

For excitation of solutes with 0-0 transitions v0o>v (antiStokes spectral region of absorption), the situation is the opposite at the initial instant of time, the spectra are red-shifted as compared to the steady state spectra, Av1 (l)<0. In this case, the return of the spectrum to its normal position during configurational relaxation will lead to a blue shift with time. From the physical point of view, this means that the intermolecular energy excess, which the solvates possess before excitation, is partially converted into emitted energy leading to an increase in the radiation frequency with time. That is why the process may be called the up-relaxation of the fluorescence spectra. 

Neither the electronic absorption nor the emission spectrum of Re2Cl8 changes in the presence of the quenchers, and no evidence for the formation of new chemical species was observed in flash spectroscopic or steady-state emission experiments. The results of these experiments suggest that the products of the quenching reaction form a strongly associated ion pair, Re2Cl8 D+. 

From the mechanism and values of the rate constants, the formation of B occurs very rapidly within a few hundred picoseconds and AB is formed on the microsecond time scale. These species exhibit characteristic absorption bands in the 550 to 600 nm region of the spectrum. At very long times, i.e. several seconds of steady state irradiation, the red shift in the absorption band is complete and presumably due to AnB as suggested by Krongauz (1 —2) Thus far, it has not been possible to clearly time resolve the formation of aggregates from AB dimers, although subtleties in the transient absorption indicate this is occurring. For instance, the time resolved buildup in absorbance at the red end of 600 nm band seems to be slower than it is 10 or 20 nm further to the blue. This may indicate a process such as ... 

Fig. 9 (A) Transient absorption spectrum of the cation radical from anthracene (AnH) in CH2C12 at about 35 ps following the 532 nm charge-transfer excitation of the 0s04 complex with 30-ps (FWHM) laser pulse. The inset shows the steady-state spectrum of AnH+- obtained by spectroelectrochemical generation. (B) The decay of the charge-transfer transient by following the absorbance at Amax = 742 nm. The inset shows the first-order plot of the absorbance decay subsequent to the maximum...

Steady-state method 2 comparison between the absorption spectrum and the excitation spectrum (through observation of the acceptor fluorescence) The corrected excitation spectrum is represented by... 

Steady-state liuninescence of topaz has been studied by Tarashchan (1978). At 77 K narrow lines at 680,696,712 and 730 nm have been ascribed to single Cr (R-Unes) and Cr +-pairs (M-lines). We studied two transparent, four yellow and one orange natural topaz. The two transparent precious stones have not been subjected to destructive chemical analyses. In other samples their Cr, Mn and V concentrations have been measured by ICP-AS method (Table 4.17). The absorption spectrvun typical for Cr + has been detected only in red topaz with the highest Cr content of 500 ppm. The spectrum clearly revealed two broad bands typical of the octahedrally coordinated Cr + (Gaft et al. 2003a). The bands centered at 418 and 533 nm evidently correspond to the spin-allowed A2g T2 and A2 transitions, respectively. The peak attributed to the spin-forbidden A2 Eg transition is located near 685 nm, while other very weak lines at 696 and 712 nm are also present. 

Fig. 23 Normalized absorption spectra of the free BSA protein (1), BSA-dye 50 conjugate (2) and steady state fluorescence emission spectrum of the BSA-dye conjugate (2 )...

Fraction of complex species in the steady state after several decaminutes the steady state appears to be reached because the d-d absorption becomes constant, as shown in Fig. 27(b), and the rate of oxygen consumption which accompanies the reaction is also held constant. The amount of Cu(II) complex (upper half of the catalytic cycle illustrated in Scheme 14) relative to Cu(I) complex (lower half of the cycle) in the steady state is determined from the ratio (absorbance of the d-d spectrum in the steady state)/(maximum absorbance immediately after substrate addition). The fraction of Cu(II) complex is also determined by magnetic measurement. The amount of substrate-coordinated Cu complex (right half of the catalytic cycle) relative to the Cu catalyst (left half) in the steady state is also obtained by spectroscopic measurement. 

The steady-state spectra obtained for different alcohols are depicted in fig. 1. While the absorption spectra red shift with increasing solvent polarisability (from methanol to octanol), the fluorescence shows a red-shift when going from octanol to methanol. The total Stokes shifts are very large 7.900 100 cm 1 for PSBR/MeOH and 6.870 100 cm 1 for octanol. Another striking observation is the 30 % smaller width of the fluorescence spectrum of methanol (AE = 3.420 cm 1) compared with other alcohols. While the widths of the fluorescence spectra are solvent-dependent, the absorption spectra have a FWHM of -5.100 cm"1, irrespective of the solvent. As we will substantiate in the following, this behavior indicates that the potential energy surface around the fluorescent point is different than near the Franck-Condon zone probed by absorption, as suggested by quantum chemistry calculations [7]. 

The steady state absorption and emission spectra of poly(A), poly(dA), and the absorption spectrum of the ribonucleotide monomer adenosine 5 -monophosphate (AMP) are shown in Fig. 1. The absorption spectra of poly(A) and poly(dA) are essentially identical. The AMP absorption spectrum is similar to the polymer spectra, but subtle differences exist. The absorption maximum of both homopolymers is shifted to the blue by several hundred wavenumbers, while the low energy band edge is red-shifted with respect to AMP. Similar shifts are observed at 77 K [15]. 

Fig. 4. (left) Transient-absorption spectra of the B-DNA helix. The dotted line is the steady-state absorption spectrum, the arrow indicates the pump frequency at 1670 cm"1, the red edge of the guanine CO-stretch band, (right) Transient-absorption spectra of the B-DNA helix. The dotted line is the steady-state absorption spectrum, the arrow indicates the pump frequency at 1685 cm 1 (the center frequency of the guanine CO-stretch band). 

The steady state absorption and fluorescence spectra of both dendrimer generations 1 and 2 are depicted in Fig. 2. The former are merely superpositions of the absorption spectra of both chromophores involved. In the fluorescence, however, the peryleneimide part is almost completely quenched compared to the model compound. Instead, the fluorescence at wavelengths longer than 650 nm almost completely resembles the emission spectrum of the terrylene-diimide model compound 3. This feature is a strong indication that within these dendrimers the excitation energy is efficiently transferred from the peryleneimide to the terrylenediimide. 

Steady-state UV-visible absorption spectrum of the NKX-2311/ZnO film is also shown in Fig. 1. It was found that adsorption of the dye onto ZnO and TiC>2 (data not shown) leads to the spectral blue-shift of the dye absorption by 15 and 25 nm, respectively, and slight broadening compared with the spectrum in solution. When a bare ZnO film (without dye) was excited at 355 nm with the nanosecond laser, an absorption band shown by the dashed line in the same figure was observed in the near IR region. This band is assigned to intra-band transitions of electrons in the conduction band [10], Electrons in Ti02 showed weaker absorption in the near IR region. 

In the conventional NMR experiment, a radio-frequency field is applied continuously to a sample in a magnetic field. The radio-frequency power must be kept low to avoid saturation. An NMR spectrum is obtained by sweeping the rf field through the range of Larmor frequencies of the observed nucleus. The nuclear induction current (Section 1.8.1) is amplified and recorded as a function of frequency. This method, which yields the frequency domain spectrum f(ai), is known as the steady-state absorption or continuous wave (CW) NMR spectroscopy [1-3]. 

The lineshape function which describes the absorption and dispersion modes of an unsaturated, steady-state NMR spectrum is proportional to the Fourier transform of the function MxID(t) (24, 25, 99)... 

Fig. 11 Illustration of the excited state relaxation derived from experimental results obtained for poly(dA).poly(dT) by steady-state absorption and fluorescence spectroscopy, fluorescence upconversion and based on the modeling of the Franck-Condon excited states of (dA)io(dT)io. In red (full line) experimental absorption spectrum yellow circles arranged at thirty steps represent the eigenstates, each circle being associated with a different helix conformation and chromophore vibrations.

Figure 5.4, one can easily understand why the interfacial electron transfer should take place in the 10-100 fsec range because this ET process should be faster than the photo-luminescence of the dye molecules and energy transfer between the molecules. Recently Zimmermann et al. [58] have employed the 20 fsec laser pulses to study the ET dynamics in the DTB-Pe/TiC>2 system and for comparison, they have also studied the excited-state dynamics of free perylene in toluene solution. Limited by the 20 fsec pulse-duration, from the uncertainty principle, they can only observe the vibrational coherences (i.e., vibrational wave packets) of low-frequency modes (see Figure 5.5). Six significant modes, 275, 360, 420, 460, 500 and 625 cm-1, have been resolved from the Fourier transform spectra of ultrashort pulse measurements. The Fourier transform spectrum has also been compared with the Raman spectrum. A good agreement can be seen (Figure 5.5). For detail of the analysis of the quantum beat, refer to Figures 5.5-5.7 of Zimmermann et al. s paper [58], These modes should play an important role not only in ET dynamics or excited-state dynamics, but also in absorption spectra. Therefore, the steady state absorption spectra of DTB-Pe, both in...

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